Fill Shikaku is a classic Japanese puzzle game available on the iPhone. The objective of the game is to divide the grid into rectangular and square pieces based on certain rules.

In Fill Shikaku, each number on the grid must be contained within a piece, which can be either a rectangle or a square. Additionally, each piece can only contain a single number, and the number represents the number of cells that must be contained within that piece.

The gameplay is simple and intuitive - players can click and drag to create rectangles and complete the puzzle. With its challenging puzzles and relaxing gameplay, Fill Shikaku is a great way to exercise your logical thinking skills and pass the time.